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This year, the sargassum along parts of Mexico's coast appears worse than it was last year. And the increased growth is not just a problem for Mexico. It affects almost all countries along the Caribbean Sea on some level.
The U.S. Gulf coast also was hit with an overload of sargassum in 2014. The seaweed invaded beaches of Florida's eastern coast in 2018. The east coast of Florida is getting hit again this year.
The seaweed is coming from Atlantic Ocean waters past the mouth of the Amazon River.
Chuanmin Hu is a professor of oceanography at South Florida University's College of Marine Science. He says the sargassum seems to be the result of increased nutrient flows from rivers and ocean water upwelling.
Upwelling is the process of cold seawater filled with nutrients rising up from the deep. Ocean currents then carry the seaweed to the Caribbean Sea, where it can grow further.
Hu says this process is unlikely to soon stop. He says more research is needed before definitely linking it all to human activity. But, he pointed to evidence of "increased use of fertilizer and increased deforestation" as possible causes, at least for the Amazon.
For now, business owners of Mexico's beach resorts are trying to find solutions.
"What you have to do is stop it before it even reaches the beaches," said Adrian Lopez, the president of Quintana Roo's employers' federation.
But, as Lopez notes, trying to collect sargassum on water could harm some sea life, such as coral that live in shallow waters close to the coast.
Removal of sargassum after it hits beaches is also risky. It could harm the sea turtle eggs or young, for example. And masses of it usually return by the end of each day anyway, Lopez explains.
Other ideas for solutions are appearing, such as using it as an additive to make bricks. But its usefulness as a fertilizer or animal feed is limited by the chemicals it contains, like salt, iodine and arsenic.
